Jen Sanders of Andersonville said she boarded the Red Line at the Argyle stop in Uptown on Friday morning and hurried off at the next stop, Lawrence, to change rail cars. The rail car reeked of feces, she said.

The "conductor made [an] announcement at Wilson or Sheridan that there must be a foul odor in a car, as many were switching cars and he saw us," Sanders, 39, told RedEye. Sanders said in the 14 years she's lived in Chicago, she's switched train cars twice because of feces.

Spotting feces on the train appears to be more of a regular occurrence lately. The jump in these incidents is a direct result of the recent record cold, when an increased number of homeless people used the round-the-clock nature of CTA service to seek shelter, agency spokesman Brian Steele said.

As a result, the CTA has increased nightly patrols with social service agencies to provide homeless people other options during unusually cold periods, Steele said. The Red and Blue lines are the only routes that run 24 hours a day.

"Our security staff, and experts from social service agencies, are working in teams to encourage homeless to take advantage of shelters and social services," Steele told RedEye.

Last week, the CTA hired 15 new rail car servicers, which brings the pool of servicers to more than 130 workers.

When a train reaches the end of the line, CTA staff walk through and clean cars before they leave on their next run. These incidents of feces are happening mid-route between the time a train leaves a terminal and arrives at the end of the line, Steele said.

If a rider spots an unsanitary condition, he or she is encouraged to inform a train operator. A rail car can be isolated from passenger use during its run and properly cleaned before returning to service, Steele said.

"As lower-than-normal temperatures abate, we expect the issue to subside, but we're going to continue our vigilance to ensure cleanliness," Steele said in an email.